Closed system

A closed system is a specific way scientists describe a physical system. In this setup, matter cannot move in or out of the system. However, energy is still allowed to pass through the system's boundaries. This exchange of energy can happen in several ways. It might move as heat or as work. Scientists use these systems to study how things change without outside matter interfering.

In the field of thermodynamics, the rules for a closed system are very specific. A closed system can exchange energy with its surroundings, but it cannot exchange matter. This is different from an open system, which can move both energy and matter. It is also different from an isolated system. An isolated system is one that cannot exchange heat, work, or matter with its surroundings.

When a system is very simple, it might contain only one type of particle. This could be a single type of atom or a single type of molecule. In these cases, a closed system maintains a constant number of those particles. However, things get more complex during a chemical reaction. During a reaction, molecules can be generated or destroyed. Even then, the system remains closed if the total number of each elemental atom stays the same.

To understand this mathematically, scientists look at the individual atoms. In a closed system, the total number of atoms for a specific element is conserved. This means the number stays constant regardless of what molecules they form. The total number of atoms is the sum of the atoms in every molecule. Because no matter enters or leaves, this total does not change. This rule allows chemists to track elements even as they change form.

Many researchers have contributed to our understanding of these systems. For example, Prigogine and Defay published work on chemical thermodynamics in the 1950s. Other scientists like Tisza and Guggenheim also provided important definitions in their books. In 1960, H.B. Callen wrote about how these terms are used in thermodynamics. It is important to note that some writers use different names. Some authors use the term "closed system" to describe what others call an "isolated system."

In the world of quantum physics, these ideas apply to very tiny scales. Scientists use Schrödinger's equation to describe a closed or isolated quantum system. This equation shows how a system behaves when it does not interchange information with another system. Information in this context includes both energy and matter. The equation uses a mathematical tool called the Hamiltonian operator. This operator characterizes the total energy of a given wave function.

Engineers also use the concept of closed systems in their work. In an engineering context, a closed system is often called a bound system. This means the system is clearly defined. In a bound system, every input is known. Additionally, every resultant or outcome is known within a specific time. This helps engineers control and predict how machines and processes will function.

Closed systems are incredibly useful for solving complex problems. By preventing matter from moving, scientists can eliminate many external factors. This simplification helps them reach thermodynamic equilibrium more easily. In chemistry, an ice cooler is a practical example of a closed system. The ice and water stay inside the cooler, but heat can still move through the walls. This allows researchers to conduct experiments where temperature is a controlled factor.